(1) Field of the Invention
This invention relates to a wireless communication system and, more particularly, to a wireless communication system in which communication data is encrypted and decrypted with an encryption key.
(2) Description of the Related Art
Recently, data is often communicated between electric devices in wireless Local Area Networks (LAN). Some wireless LANs are composed of client terminals such as personal computers with a wireless communication function and access points for connecting the client terminals to wired LANs by communicating with the client terminals by radio. The client terminals communicate with each other by radio, and are connected to wired LANs via the access points by radio. The access points are connected to each other, via wired LANs with the infrastructure method or via wireless LANs with the wireless distribution system.
In the wireless communication, data should be made confidential with encryption in case of interception of the data. In the wireless LANs, data is encrypted with an encryption key which should be shared by communicating parties. Therefore, an encryption key to be shared is set at client terminals and access points composing a wireless communication system, at the initial setting.
By intercepting and analyzing encrypted data in the communication area of a wireless LAN, the third party may obtain an encryption key which is used in this area. To prevent this happening, an encryption key update system including a key management server being connected to access points in a LAN has been proposed, in which the key management server sends a new encryption key to each access point and wireless terminal when updating an encryption key (for example, refer to Japanese Unexamined Patent Publication No. 2001-111543 (paragraph [0035] to [0041], FIG. 1)). This encryption key update system is capable of improving security by updating an encryption key.
As another system, a wireless communication system has been proposed, in which indexable encryption keys are stored in terminals and access points and an access point sends index information on a selected encryption key to a terminal, so that the terminal can use the encryption key based on the index information (for example, refer to Japanese Unexamined Patent Publication No. 2003-258790 (paragraph [0022] to [0024], FIG. 1)). This wireless communication system is capable of improving security by changing an encryption key.
On the other hand, there has been proposed an authenticating method in a wireless LAN system which can concurrently achieve delivery of an encryption key for maintaining concealment between only communicating parties and an authenticating procedure (for example, refer to Japanese Unexamined Patent Publication No. 2003-5641 (paragraph [0033] to [0037], FIG. 1).). This authenticating method in a wireless LAN system is capable of simplifying second and following authenticating procedures to identify the same access point after releasing the authentication.
The aforementioned first encryption key update system according to Japanese Unexamined Patent Publication No. 2001-111543, however, has a large-scale problem because of the key server which should be installed on a wired LAN to update an encryption key.
Further, the aforementioned second wireless communication system according to Japanese Unexamined Patent Publication No. 2003-258790 has a problem in which the third party may know what encryption key is being used, by intercepting index information which is sent from an access point to a terminal to index an encryption key.
Still further, the aforementioned third authenticating method according to Japanese Unexamined Patent Publication No. 2003-5641 has a problem in which the third party may know an encryption key because the same encryption key is used after the first authentication.